Closing down Windows apps used to be pretty simple. Just look for the big red 'X,' click, and be done with it. Windows 8, on the other hand, tries to encourage users to keep apps running in the background, drawing some resources, but also being quickly accessible. While many desktop apps can be closed traditionally with the 'close' button and "ALT+F4," Metro apps can be a mixed bag. If you really feel the need to kill a Metro App, you can try:
-The App Control bar
-Mousing over the top of the screen, and then click-dragging to the bottom of the page.
-Bringing up the Open Apps sidebar (left of screen), and then right clicking on an open app to close it.